1. Field of the Invention
The invention relates to the use of copolymers with vinyl-functionalized and styrene-oxide-based polyethers for preparing aqueous pigment preparations.
2. Discussion of the Art
In order to facilitate and to improve the dispersion of solids in liquid media it is common to use dispersants, which as surface-active agents promote wetting of the particulate solids to be dispersed, and aid in the disruption of agglomerates. These dispersants also have a stabilizing effect on the resultant dispersions and prevent reagglomeration or flocculation of the particulate solids. Dispersants are particularly important, for example, for dispersing pigments in the preparation of printing inks, paints and other coating materials.
In the preparation of inks and paints, wetting agents and dispersants facilitate the incorporation of pigments and fillers, which are important formulating constituents that significantly determine the visual appearance and the physicochemical properties of coatings. Optimum use requires firstly that these solids are distributed uniformly in paints and inks, and secondly that the state of distribution, once attained, is stabilized. Numerous problems may occur during the preparation and processing of aqueous pigment pastes and their subsequent use in formulating paints and inks:    high color paste, ink and paint viscosities    sedimentation    vertical separation of pigments (flooding)    horizontal separation of pigments (floating)    low degree of gloss    low hiding power    inadequate transparency    inadequate color strength    poor shade reproducibility, shade shift    excessive tendency of coating materials to run
There has therefore been no lack of attempts to provide effective dispersing additives for solids, especially pigments. For example, water-soluble polyisocyanate adducts containing hydrophilic polyether chains (EP-A-0 731 148), acid poly(meth)acrylates (U.S. Pat. No. 3,980,602; WO-A-94/21701), phosphate esters of polyalkylene oxide block polyesters (WO-A-97/19948), amine oxides (DE-A-199 04 603) or alternating copolymers of vinyl monomers and dicarboxylic diesters (especially copolymers based on maleic acid derivatives and vinyl monomers) are described for this purpose (WO-A-96/14347, EP-A-0 791 024).
However, the use of such products is also associated with a multiplicity of disadvantages. Frequently, for instance, large amounts of dispersing additives are required; the levels of paste pigmentation that can be achieved are unsatisfactorily low; or the stability of the pastes and hence the consistency of their viscosity is inadequate. Flocculation and aggregation cannot always be avoided. The dispersion of hydrophobic organic pigments, in particular, causes problems in numerous instances. There is often a lack of consistency of shade following storage of the pastes, and a lack of compatibility with a variety of binders. In many cases, the use of known dispersing additives also has an adverse effect on the water resistance or light stability of coatings and, moreover, provides additional stabilization of the unwanted foam which is formed in the course of the preparation and processing. Furthermore, owing to deficiencies in the compatibility of the dispersing additives in numerous letdown binders, there is often an undesirable impairment—that is, lowering—of the gloss.